Description

The purpose of this technique is to allow there to be more audio description
than will fit into the gaps in the dialogue of the audio-visual material.

With SMIL 2.0 it is possible to specify that particular audio files be
played at particular times, and that the program be frozen (paused) while
the audio file is being played.

The effect is that the video appears to play through from end to end but
freezes in places while a longer audio description is provided. It then
continues automatically when the audio description is complete.

To turn the extended audio description on and off one could use script to
switch back and forth between two SMIL scripts, one with and one without the
extended audio description lines. Or script could be used to add or remove
the extended audio description lines from the SMIL file so that the film
clips would just play uninterrupted.

If scripting is not available then two versions of the SMIL file could be
provided, one with and one without extended audio description.